The invention relates to a clock signal generator mechanism, and more particularly to a quadrature clock signal generating apparatus and a communication system transmitter.
Generally speaking, a conventional local oscillator signal generator is used for generating quadrature clock signals by adopting an oscillator to generate a clock signal and an inverted clock signal, using a phase generator for generating clock signals with different phases, and finally using a phase selecting circuit to select clock signals with appropriate phases as its outputs. However, the generated clock signals with different phases correspond to a high frequency which requires that the circuit elements operate at a higher frequency and inevitably increases higher power consumption. In addition, it is easier to introduce delay mismatch for the signals. Also, a timing circuit within the conventional local oscillator signal generator needs to operate at a particular frequency range, and it is more difficult to guarantee the functionality of the timing circuit when the conventional phase selecting circuit is used on corner variation. For example, the functionality of the timing circuit may be significantly affected if the operation rate/frequency of such timing circuit does not fall within a frequency range corresponding to a range from 0.75 times TCK to one TCK wherein TCK means the period of a clock signal generated by a local oscillator.
Further, another conventional scheme may adopt a calibration mechanism to obtain excellent spur performance but also encounters the problems of higher power consumption and difficulty of guaranteeing the functionality of a timing circuit. Also, this conventional scheme does not generate and provide quadrature signal outputs.
Further, for an IoT (Internet of Things) application such as a Bluetooth system, in order to avoid signal pulling from a power amplifier, it is needed to design or configure the frequency of an output signal generated by a local oscillator to be not equal to an integer multiple of the local clock signal inputted to a local mixer. However, a conventional clock signal generator with a fractional divider inevitably consumes more power than a conventional clock signal generator with an integer divider, and low power consumption is critical requirement for such IoT application.